President Barack Obama has called on Moamer Kadhafi to "leave now," declaring that the Libyan leader had lost his right to rule after attacking his own people to put down a popular uprising.
Obama's most direct demand yet that Kadhafi step down was made in a telephone call with German Chancellor Angela Merkel to coordinate their response to the crisis, the White House said.
"The president stated that when a leader's only means of staying in power is to use mass violence against his own people, he has lost the legitimacy to rule and needs to do what is right for his country by leaving now," it said.
Hours later, the UN Security Council voted unanimously to order an investigation into crimes against humanity, an arms embargo and travel bans and asset freezes targeting Kadhafi, his family and inner circle.
The resolution cited "gross and systematic violation of human rights, including the repression of peaceful demonstrators" and incitement to hostility and violence "from the highest levels of the Libyan government."
The UN resolution stopped short of demanding Kadhafi's removal from power, something that Obama had also refrained from doing while US citizens were being evacuated from Libya.
But the president and Secretary of State Hillary Clinton sharply changed tack Saturday in back-to-back statements.
"Moammar Qadhafi has lost the confidence of his people and he should go without further bloodshed and violence," Clinton said, using an alternate spelling for Kadhafi.
"The Libyan people deserve a government that is responsive to their aspirations and that protects their universally recognized human rights."
The diplomatic moves came as Kadhafi hunkered down in Tripoli for what many feared would be a bloody showdown with rebels that have taken control of large areas of the oil-rich North African country.
The Libyan leader's son, Seif al-Islam Kadhafi, earlier told Al-Arabiya television that the crisis had "opened the doors to a civil war."
As the impasse deepened, thousands of foreign workers were trying to flee the country and embassies closed their doors. The United Nations estimates that more than 1,000 civilians have been killed so far.
The White House said Obama and Merkel "discussed appropriate and effective ways for the international community to respond."
"The president welcomed ongoing efforts by our allies and partners, including at the United Nations and by the European Union, to develop and implement strong measures," the statement read.
On Friday, Obama announced unilateral sanctions targeting Kadhafi and his inner circle in a move intended to encourage defections and peel away loyalists defending the Libyan's 42-year rule.
These included orders to seize Kadhafi family assets in the United States, suspend military sales, and travel restrictions targeting regime officials.
Clinton said she had signed an order revoking the US visas of Libyan officials and others linked to the violence against civilians. She said new visas would be denied as a matter of policy.
The US intelligence agencies, meanwhile, were ordered to gather information on atrocities that could be used as evidence, and the US financial system was told to watch out for movements of funds from Libya.
"We are moving quickly on a series of steps to hold the Libyan government accountable for its violation of human rights and to mobilize a strong response from the international community," Clinton said.
"Consistent with the president's guidance, we will continue to look at the full range of options to hold the Libyan government accountable and support the Libyan people," she said.
A leading Republican, Representative Ileana Ros-Lehtinen, who chairs the House Foreign Affairs Committee, said the sanctions announced Friday were "a positive first step."
But she said stronger penalties were needed to hold the Kadhafi regime accountable.
The Florida congresswoman said additional US and international measures should include a no-fly zone, a comprehensive arms embargo, a travel ban, suspension of all contract and assistance that benefit the regime, and restrictions on foreign investment.
In Chicago, hundreds of protesters took to the streets Saturday to voice their disgust with Kadhafi's deadly crackdown.